Study On Structure Regulation And Lithium Storage Properties Of Anthraquinone-based Covalent Organic Framework

As an emerging class of crystalline organic material,covalent organic frameworks（COFs）have shown great potential as high-performance electrode materials for metal-ion batteries in view of their relatively high capacity,flexibly designable structure,ordered porous structure.However,the conductivity of COFs is relatively low,resulting in poor rate performance at high current density.It is difficult for metal ions to reach deep buried active sites,which reduces the electrochemical activity and hinders their practical application.Therefore,this paper uses 2,6-diaminoanthraquinone（DAAQ）as the energy storage unit of COFs.The conductivity of COFs was improved by iodine doping strategy.The molecular structure of COFs was designed by selecting different connection units to promote the transport of charge and ions,enhance lithiumion storage,and improve the capacity and rate performance of anthraquinone-based COFs electrode materials.The main research contents are as follows:1.Iodine-dopedβ-ketoenamine COF/COF-I₂ was successfully prepared by adding iodine,TFP and 2,6-diaminoanthraquinone（DAAQ）during the synthesis of COFs by a simple solvothermal method.The results show that the iodine anion in the framework can effectively attract Li⁺ions through electrostatic interaction,which improves the lithium affinity of the COFs pore wall and gives COFs more accessible active sites and higher electronic/ionic conductivity.Therefore,after 1000 cycles at a current density of0.2 A g^-1,COF-I₂ still has a high specific capacity of 140 m Ah g^-1,a capacity retention rate of 89%,and shows good rate performance,which is much higher than that of the pure COF.Therefore,in-situ doping of iodine with strong electronegativity can increase the surface defects of COFs,promote the diffusion of ions/electrons,and improve the conductivity and structural stability of its composites.This work provides a simple method for the development of high-performance anthraquinone-based COFs electrodes.2.Anthraquinone-based TFP_X-COFs containing two different bonding modes（imine-type andβ-ketoenamine-type）were prepared using solvothermal method by regulating the molar ratio of the connecting unit TFP and TFB（trimesic aldehyde）.The results show that the intramolecular hydrogen bond is formed between the electron-withdrawing group C=O and the H on the amino group in the COFs layer,which makes the partial structure of the internal system’locked’,reduces the rotational freedom of the flexible unit inside the COFs,increases the flatness of the 2D layer,and improves the degree of structural order,so that the TFP-COF with the highest hydrogen bond content has great crystallinity.At the same time,due to the formation of intramolecular hydrogen bonds,the redox activity of the carbonyl group is reduced,which affects its electrochemical performance.Consequently,TFB-COF electrode with the lowest hydrogen bond content exhibits excellent cyclic stability for more than 500 cycles at0.2 A g^-1,the initial discharge specific capacity of 150 m Ah g^-1,and the coulomb efficiency of 99.98%.At a high rate of 1 A g^-1,the discharge specific capacity is maintained at 138 m Ah g^-1.Therefore,the COFs materials with specific crystallinity and electrochemical properties can be obtained by adjusting the molecular structure of organic materials,which provides a new idea for the development of high-performance COFs-based lithium ion batteries（LIBs）cathode materials.